This invention relates to an improved fluidized bed process.
Fluidized bed processes are used commercially for the chlorination of titanium containing materials, ore roasting or refining, combustion of solid carbonaceous material such as coal, etc.
In such processes, particulate material, air, oxygen or other oxidizing agents are fed into a reaction chamber, and suitable temperature and pressure are maintained. The flow rates are adjusted so that the particulate material becomes fluidized, i.e., it is maintained in a state of suspension and has the appearance of boiling.
A good example of a commercial fluidized bed process is that for chlorinating titanium containing material. In such process, particulate coke, particulate titanium containing material, chlorine and optionally oxygen or air are fed into a reaction chamber, and a suitable reaction temperature, pressure and flow rates are maintained to sustain the fluidized bed. Gaseous titanium tetrachloride and other metal chlorides are exhausted from the reactor chamber. The gaseous titanium tetrachloride so produced can then be separated from the other metal chlorides and used to produce titanium dioxide pigment or titanium metal.
A problem, however, which has not been satisfactorily solved in the foregoing fluidized bed processes is that particulate material of fine size tends to becomes entrained in the hot gases exiting the process. As a consequence, such fine particulates have a short residence time in the reaction zone of the process, and often exit the reactor in an unreacted state. While the fine particulates can be recycled to the process, they still tend to exit before reacting and therefore generally must be removed from the process. The unreacted fines therefore are a disposal problem and a waste of the fuel, metallic, or other values in the materials being processed.
The fine particulate material typically is present due to the attrition and degradation of particulate materials of larger particle size which are fed to the fluidized bed process. However, it would be desirable to be able to feed fine particulate material to the process because it often is abundant and less expensive than materials having larger particle size. For example, there exists abundant quantities of relatively inexpensive titanium containing ore which currently cannot be economically processed because it exists in the form of sands having small particle size.
The following references are disclosed as being of interest to the subject matter of this invention:
U.S. Pat. No. 2,701,179 discloses a commercial fluidized bed process for chlorinating titanium containing material wherein the particulates are fed pneumatically with chlorine into the bottom of the fluidized bed reactor.
An article entitled, "Fluidized Bed Chlorination of Rutile", by J. Glasser and W. L. Robinson, appeared in the Sep. 9, 1962 publication of the Society of Mining Engineers of AIME. It describes a commercial fluidized bed process for chlorinating titanium containing ore wherein course particulate ore of a size greater than about 70 microns is fed to the top of a fluidized bed reactor.
U.S. Department of Energy Contract Report Fe-21063-8-1985, by W. C. Yang, and entitled, "A Study of Fine Particle Residence Time in a Jetting Fluidized Bed", discloses laboratory scale fluidized bed experiments including injecting fine particulate acrylic material into and above the fluidized bed. The experiments appear to conclude that (a) coaxial pneumatic injection below the bed is less desirable than radial pneumatic injection above or below the bed, and (b) radial pneumatic injection above and below the bed produced similar results.
An article entitled, "Fluid Bed Behavior in Zinc Roasters", by N. J. Themelis and G. M. Freeman appeared in the August 1984 issue of the Journal of Metals. It discloses the commercial fluidized bed roasting of zinc ores wherein the ore is fed to the reactor above the fluidized bed.
The U.S. Bureau of Mines report No. 8165 was authored by H. M. Harris, A. M. Henderson and T. T. Campbell. It is entitled, "Fluidized Coke Bed Chlorination of Ilmenites" and discloses pneumatic feed, below the fluidized bed, of titanium containing ores and coke. A laboratory scale reaction is used.